Synthesis and structure of trans -[[[cis -tetracarbonylbis (N-((2-diphenylphosphinamido)ethyl)salicylaldimino-P)]molybdenum(0)]-N,-N′ ,O,O′]nickle(II), a novel bimetal trans-ligating tetradentate schiff base complex with a "fly-over" chain containing a metal atom